Piles are generally well known structures for establishing offshore foundations.
Recently offshore wind power has become more and more popular and important. Generally offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Offshore wind farms include fixed-bottom wind turbine technologies in shallow water areas, often referred to as near shore wind power. Wind turbines and electrical substations are typically arranged on so called monopile foundations or jacket foundations or tripods or the like which are fixed on the seabed in shallow water subsea locations. Many offshore wind farms utilize monopile foundations. Monopiles are normally steel tubes or steel pipes of large diameter, for example with a diameter of about 4 m which are sunk 25 m deep into the seabed. The piles are normally rammed or vibrated or drilled into the seabed. Generally the load bearing capacity of a driven pile depends on its embedded length and the compression of the surrounding soil. The more friction acts on the sides of the pile the bigger is the load bearing capacity.
Of course the load bearing capacity also depends on the buckling resistance of the pile itself and on erosion around the pile incurred by currents and waves. Wave-slamming has also to be considered when calculating the load bearing capacity of the pile. Generally piles are driven into the seabed by impact driving or by vibrating or by combinations thereof.
Since each proposed construction site for offshore structural foundations can have different geological ground conditions there are certain design constrains as regards the stability of the pile in terms of wall thickness and choice of material. For example the wall thickness must be chosen so that the pile can withstand increased impact driving forces in the event of a non-expected increased driving resistance of the seabed. Generally it would be desirable to install monopiles with a reduced embedded depth, however this would mean that the diameter would have to be increased in order to avoid the risk of buckling. This however increases transportation and handling costs.